Imaging apparatus and method for controlling same

ABSTRACT

To provide an imaging apparatus and a method of controlling the apparatus that enables improved automatic focus adjustment performance also in relation to an image having a shallow depth of field. An imaging element  103  includes a focus state detection unit for detecting a phase difference. A camera signal processing unit  106  generates a focus adjustment signal based on the imaging signal and outputs the signal to a camera control unit  109 . The camera control unit  109  acquires an in-focus lens position in accordance with a focus lens based on a focus deviation amount based on a focus state detection result, calculates distance information related to the in-focus distance on the image screen, and controls the driving of the focus lens  102  based on the distance information and the focus adjustment signal from the camera signal processing unit  106 . When a difference between the in-focus lens position and the position of the focus lens at the current time exceeds a threshold, the camera control unit  109  drives the focus lens to the in-focus lens position based on the distance information. When the difference between the in-focus lens position and the focus lens position at the current time is less than or equal to the threshold, the camera control unit  109  executes the in-focus control based on the focus adjustment signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to focus adjustment control for an imagingapparatus.

2. Description of the Related Art

The introduction of single-lens reflex cameras has generated theopportunity to capture moving images with a large imaging sensor (forexample, a 35 mm full-size sensor). Since a large sensor exhibits ashallow depth of field in comparison to small sensors that are used inconventional video cameras, blurring of an image may result. Therefore,in addition to in-focus areas of the image, prominent out-of-focus areasin the image are a cause of concern, and therefore there is a demand forfurther improvement to auto-focus adjustment.

A so-called TV-AF (autofocus) method is known as an auto-focusadjustment method during capture of moving images in which the sharpnessof the imaging signal is evaluated. In this method, focus positionshaving the highest apparent focus are searched and extracted in order toevaluate the sharpness of the imaging signal itself. However, since theabsolute defocus amount is not known, time is required to reach thein-focus point. In other words, acquisition of the in-focus point isretarded since the in-focus direction is only known from informationrelated to the focus lens position in that time range and the differencein the level of the TV-AF signal. The focus lens must be constantlymoved to compare with the level of the TV-AF signal, and thereforechanges in the degree of blurring in the resultant image are emphasizedparticularly in objects that are removed from the depth of field.

A method has been proposed for detecting a focus state by applying apupil division to a light flux in pixels in a portion of an imagingsensor and causing the divided light flux to become incident upon a pairof detection pixels (refer to Japanese Patent Laid-Open No.2000-292686). Currently, progress in improved pixelation and theincreasing size of imaging sensors have enabled the incorporation offocus state detection areas into a plurality of areas in the screen. Inthis manner, since a defocus amount of each area is discernable, thedistance to an object to be imaged can be known in relation to each areain the screen. However, since the pixels in a portion of the imagingsensor are used as detection pixels, that is to say, as focus statedetection elements, image data in relation to that portion must begenerated by an image interpolation process, or the like. Therefore,there is a risk that the captured image will be degraded by an increaseddensity caused by disposing a detection element on the whole effectivepixel region in order to increase the focus detection accuracy.

A conventional automatic focus adjustment apparatus cannot realize anautomatic focus adjustment capability that is adapted to an imagingsystem that has a shallow depth of field. As a result, a conspicuouschange in an amount of blurring results in a TV-AF method, and whenusing a configuration in which a focus state detection element isincorporated into the imaging sensor, if the arrangement density of thedetection elements is reduced to prevent image quality degradation, asufficient detection accuracy is not obtained.

SUMMARY OF THE INVENTION

The present invention provides an imaging apparatus that includes animproved automatic focus adjustment also in relation to an image havinga shallow depth of field, and a method for controlling the same.

In order to provide a solution to the above circumstances, the apparatusaccording to the present invention includes a focus state detection unitprovided in an imaging element for detecting a phase difference, asignal processing unit for generating a focus adjustment signal based onthe imaging signal outputted by the imaging element, and a control unitthat acquires an in-focus lens position in accordance with a focus lensbased on a focus deviation amount that is calculated from a detectionresult of the focus state detection unit to thereby calculate distanceinformation related to the in-focus distance on the image screen, andthat controls the driving of the focus lens based on the distanceinformation and the focus adjustment signal. When the difference betweenthe in-focus lens position and the position of the focus lens at thecurrent time exceeds a threshold, the control unit drives the focus lensto the in-focus lens position, and when the difference between thein-focus lens position and the focus lens position at the current timeis less than or equal to the threshold, the control unit executes thein-focus control based on the focus adjustment signal.

According to the present invention, improved automatic focus adjustmentperformance is provided also in relation to an image having a shallowdepth of field by parallel application of distance information obtainedfrom phase difference detection, and a focus adjustment signal based onan imaging signal.

Further features of the present invention will become apparent from thefollowing description of embodiments with reference to the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a configuration of an imaging apparatusaccording to a first embodiment of the present invention.

FIG. 2 illustrates an example of an imaging element that enablesacquisition of distance information in addition to image information foran object.

FIG. 3 illustrates a basic principle of a phase difference detectionmethod and a pupil division method in relation to a micro-lens in theimaging element.

FIG. 4 illustrates an example of a configuration of a camera signalprocessing unit and a camera control unit to describe the firstembodiment of the present invention by reference to FIG. 5 to FIG. 10.

FIG. 5 illustrates an example of an interpolation processing methodrelated to a detection element for phase difference detection.

FIG. 6 illustrates an example of a detection frame and a distance map.

FIG. 7 is a flowchart that describes the flow of auto-focus control.

FIG. 8 is a flowchart that describes the TV-AF control in FIG. 7.

FIG. 9 is a flowchart that describes a control example related to minutedriving in FIG. 8.

FIG. 10 illustrates an example of the detection frame and distanceinformation.

FIG. 11 is a flowchart that describes a control example related tohill-climbing driving in FIG. 8.

FIG. 12 illustrates an example of a configuration of a camera signalprocessing unit and a camera control unit according to a secondembodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIG. 1 illustrates an example of a configuration of a video cameraaccording to a first embodiment of the present invention. In the presentembodiment, although a video camera is described as an example of animaging apparatus, the present invention may be applied to other imagingapparatuses such as digital still cameras.

The imaging optical system illustrated in FIG. 1 only illustrates a zoomlens (variable power lens) 101, and a focus lens 102. The focus lens 102is a focus adjustment lens or lens group that includes a focusingfunction. An imaging element 103 is a photoelectric conversion devicesuch as a complementary metal-oxide semiconductor (CMOS) imaging sensoror the like, and converts and outputs a light receiving signal as anelectrical signal. An analog signal processing unit 104 processes anoutput signal of the imaging element 103 to thereby execute gainadjustment, or the like. An A/D conversion unit 105 converts theanalogue signal output by the analog signal processing unit 104 to adigital signal. The camera signal processing unit 106 executes varioustypes of image processing on the A/D converted digital signal andgenerates a video signal for output to a display unit 107 and a storageunit 108. The camera signal processing unit 106 includes a TV-AF signalprocessing circuit as described below, and generates a signal byextraction of high-frequency components from the video signal inaccordance with a predetermined region in the screen, that is to say,generates a TV-AF signal. The TV-AF signal is output to the cameracontrol unit 109.

The display unit 107 is configured by a liquid crystal display (LCD) orthe like, and displays an image upon receipt of a video signal from thecamera signal processing unit 106. The storage unit 108 processes thevideo signal from the camera signal processing unit 106 for storage in apredetermined format in a storage medium (magnetic recording medium orsemiconductor memory, or the like).

The camera control unit 109 executes operational control for the wholevideo camera and acquires the TV-AF signal from the camera signalprocessing unit 106. The camera control unit 109 incorporates the pixel(focus state detection element) output used in phase differencedetection by the imaging element 103 into an output signal for twoimages described below (image A and image B), performs a calculation forphase difference detection, and thereby acquires a focus deviationamount for each portion of the imaging area. The camera control unit 109during AF control shifts the focus lens 102 to the in-focus lensposition based on the TV-AF signal, the map information (distance map)displaying the distance distribution acquired by phase differencedetection, and the in-focus position according to a distance map. Thecamera control unit 109 controls the driving of the zoom lens 101, thedriving of the imaging element 103, and the like.

FIG. 2 illustrates an example of the configuration of an element adaptedfor imaging in the imaging element 103, and a focus state detectionelement for phase difference detection. As illustrated in the enlargedview, the element adapted for imaging and the focus state detectionelement are arranged in series. In this example, elements illustrated asrespective pixel columns in the first and second row, and the fourth andfifth row (indicated by the square in the round frame) are used forimaging. Detection elements for the imaging position illustrated in thesecond column, sixth column and tenth column . . . of the third row (thetwo rectangles in the round frame) are used for focus state detection.The focus state detection element exhibits improved detection accuracywhen in a continuous configuration. However, since the image issubjected to a large degradation, there is a trade-off between improvingaccuracy and high pixelation. A micro-lens is disposed as illustrated bythe round frame on the pre-surface of each element to execute highlyefficient collection of incident light.

In the focus state detection element, each divided light flux isrespectively incident upon the pair of light receiving elements A and Bby subjecting the light flux to pupil division as shown in FIG. 3A. Thedetection result of each element is configured by combining each outputof the light receiving element A (refer to the rectangles on the leftside of the round frame) that is arranged in series in the horizontaldirection as shown in FIG. 2 to form a first image (hereinafter referredto as “image A”). Furthermore, the output of each light receivingelement B (refer to the rectangles on the right side of the round frame)is combined to form a second image (hereinafter referred to as “imageB”).

Next, the focus detection principle used to acquire a focus deviationamount for the imaging lens from image A and image B will be described.As illustrated in FIG. 3B, the position of the object image (image A)formed on the imaging plane by the light flux that passes through regionA of the photographic lens and the object image (image B) formed by thelight flux that passes through region B changes in response to thein-focus time, the front focus time, and the rear focus time. As thedefocus amount that is the distance between the image-forming surfaceand the imaging plane increases, the deviation between image A and imageB increases, and the reference numeral for the deviation amount isreversed during front focus and rear focus. The use of the imagedeviation to detect a defocus amount configures a phase differencedetection method.

Next, using FIG. 4, the processing executed by the camera signalprocessing unit 106 (refer to reference numerals 501 to 504) and thecamera control unit 109 (refer to reference numerals 506 to 512) will bedescribed.

The imaging signal read from the imaging element 103 causes a signalloss in the pixel portion corresponding to the position of the focusstate detection element. For this reason, a pixel interpolationprocessing unit 501 calculates data corresponding to the position of thefocus state detection element by interpolating using data for an imagethat is positioned on the periphery of the focus state detectionelement. The output signal of the pixel interpolation processing unit501 is sent to the video signal processing unit 502, and is handled bythe video signal processing circuit 6. This method of interpolationcalculation as illustrated in FIG. 5 includes a process in which thesignals from pixels having the same color, and positioned in a verticalconfiguration in relation to the target focus state detection elementare processed using a simple average. In the present example, the focusstate detection element is positioned in the center of a 5-row 5-columnconfiguration, and “Exx” (x=1 through 5) expresses the load level foreach pixel. When using a simple average method, the value E33 at theposition of the focus state detection element is calculated as theaverage value of E31 and E35 that are positioned vertically by onepixel. In addition, a range of other methods of calculation may be usedincluding a method of calculating a weight average value using data forthe load level of a larger number of pixel that are positionedvertically and transversely with respect to a central positionconfigured by the focus state detection element. Since this method isalready known as a technique that is the same as image defectcorrection, detailed description thereof will be omitted.

The auto-focus (AF) gate switch 503 indicates an ON/OFF switch sign asillustrated in FIG. 4 and enables the selection of the portion of theimaging signals converted by the A/D conversion unit 105 for AF signalprocessing. The AF gate switch 503 is controlled according to a signalfrom the AF control unit 512 described below. The TV-AF signalprocessing unit 504 acquires a value that expresses the sharpness of theimage by application of a bandpass filter or the like to a signalextracted using the AF gate switch 503 to thereby extract frequencycomponents within a predetermined range. The video signal processingunit 502 processes the video signal to generate a signal that can behandled by the display unit 107 and the storage unit 108 in subsequentstages (refer to image data 505).

Next, the process for generating a TV-AF signal as a focus adjustmentsignal will be described. A TV-AF signal is generated for example bycalculating the level of predetermined high-frequency components using afiltering process on the imaging signal. At this time, a distance mapdetermines what portion of the TV-AF signal in the screen should beacquired. When a filtering process is executed on a signal that includesdefective pixel portions corresponding to the position of the focusstate detection element, the resulting signal will include errors.Consequently, the AF gate switch 503 controls AF signal processing inrelation to a portion or portions of the video signal. In other words,in addition to determination of the AF area, the switch has the role ofeliminating horizontal lines of the video signal that includes defectivepixel portions corresponding to the position of the focus statedetection element and which, as a result, cannot pass through TV-AFsignal processing. In this manner, a TV-AF signal that is free of theeffect of defective pixel portions corresponding to the position of thefocus state detection element can be obtained.

A selector 506 that is denoted by the reference symbol for the switch inthe camera control unit 109 allocates signals of the imaging signalssubjected by A/D conversion by the A/D conversion unit 105 to the imageA and the image B described above. In other words, when the selector 506has switched to a first state, data for the image A is acquired by thephase-difference calculation processing unit 507, and when the selector506 has switched to a second state, data for the image B is acquired bythe phase-difference calculation processing unit 507. Thephase-difference calculation processing unit 507 calculates thedimension of a deviation amount in the image A and the image B for eachposition in the image screen, and processes the deviation amount at eachdetection position in the form of two-dimensional array data as shown bythe table 508.

A distance map generation processing unit 509 calculates an in-focuslens position based on the deviation amount calculated by thephase-difference calculation processing unit 507, and calculates anin-focus distance for each area in the image screen using the in-focuslens position and the distance table 510. The camera control unit 109for example retains the in-focus distance data corresponding to discretefocus lens positions for each zoom lens position in the data formatillustrated in the distance table 510. The distance map generationprocessing unit 509 uses the data in the distance table 510 tointerpolate the in-focus distance corresponding to the focus lensposition, and thereby generates a distance map by calculation of thedistance information to the object for each focus state detection areaon the imaging screen. The calculation result is managed in the form oftwo-dimensional array data as illustrated by the table 511.

The AF control unit 512 executes in-focus control by driving the focuslens 102 based on the data in the distance map and the TV-AF signal.

FIG. 6 illustrates an example of the distance map and the detectionframe for the focus state. In the example illustrated in FIG. 6A, themost frequent distance to the proximity of the screen central portion isdetermined. In other words, the data element (1.4 meters) illustrated inthe rectangular frame is the most frequently occurring data in thedistance data illustrated in the frame enclosed by the broken line. Asillustrated in FIG. 6B, an area centering on this distance from withinthe depth of field (in the example, the range of 1 to 2 meters) is setas the detection frame (TV-AF frame). At this time, the camera controlunit 109 determines the proportion of the area that is increased byincreasing the TV-AF frame and the area within the depth contained inthe frame. When the proportion of the area within the depth is reduced,the frame size is set to prevent the TV-AF frame from increasing. Inthis manner, even when positioned is removed at a distance within thedepth by a single position, an excess increase in the detection framecan be prevented.

The focus adjustment control executed by the AF control unit 512 will bedescribed using the flowchart in FIG. 7 to FIG. 9, and FIG. 11. Theprocessing executed during AF control is executed by programs andinterpreted by the computer that configures the camera control unit 109.

Processing is commenced in step S801 in FIG. 7 and TV-AF control isexecuted in step S802. The details of control will be described belowusing FIG. 8. Step S803 is a process of setting the lens positiondifference. The set value for the lens position difference (denoted as“th”) is a reference value (threshold) for determining whether or not toshift the focus lens 102 to the in-focus position in accordance with thedistance map when a difference is identified between the in-focusposition according to the distance map and the current lens position.The camera control unit 109 in step S804 compares the difference betweenthe in-focus position according to the distance map and the current lensposition with the th value set in step S803. When the difference betweenthe in-focus position according to the distance map and the current lensposition (absolute value) is greater than the th value, the processproceeds to step S805. When the determination condition in step S804 isnot satisfied, and the lens position difference is less than or equal tothe threshold value, the processing returns to step S802, and processingis continued. The camera control unit 109 in step S805 executes drivecontrol for the focus lens 102 and shifts the focus lens 102 to thein-focus position calculated with reference to the distance map.

Next, the TV-AF control in step S802 above will be described withreference to the flowchart in FIG. 8. The processing is commenced instep S901, and minute driving of the focus lens 102 is executed in stepS902. Minute driving is driving of the lens by searching points inproximity to the in-focus point to thereby perform an in-focusdetermination or discriminate the direction. The details of such drivingcontrol will be described below with reference to the flowchart in FIG.9. The camera control unit 109 determines in-focus in step S903, andwhen it is determined that the apparatus is in-focus, the processproceeds to step S909. When it is determined that the apparatus is notin-focus, the process proceeds to step S904, and discrimination of adirection that coincides with in-focus is executed.

The camera control unit 109 in step S904 proceeds to step S905 when adirection is discriminated by driving the lens in step S902. However,when a direction has not been discriminated, the processing returns tostep S902, and minute driving is continued. The camera control unit 109in step S905 shifts the focus lens 102 at high speed in a direction inwhich the level of the TV-AF signal is increased, that is to say,hill-climbing driving is executed. The details of the driving andcontrol process will be described below with reference to the flowchartin FIG. 11.

The camera control unit 109 in step S906 determines whether or not thelevel of the TV-AF signal has exceeded the corresponding peak value.When it is determined that hill-climbing driving has caused the level ofthe TV-AF signal to exceed the corresponding peak value, the processproceeds to step S907. When it is determined that the level of the TV-AFsignal has not exceeded the corresponding peak value, the processingreturns to step S905, and the camera control unit 109 continueshill-climbing driving.

The camera control unit 109 in step S907 returns the lens position ofthe focus lens 102 so that the level of the TV-AF signal duringhill-climbing driving re-approximates the peak value. The next step S908is a determination process of whether or not the level of the TV-AFsignal exhibits a peak value. When it is determined that the position ofthe focus lens 102 has returned to a lens position that exhibits a peakvalue, the camera control unit 109 returns processing to step S902, andminute driving is executed again. Conversely, when the position of thefocus lens 102 has not returned to a lens position that exhibits thepeak value, processing returns processing to step S907, and theoperation is continued.

Next, the in-focus operation that is executed when a determination thatthe configuration is in-focus is provided in step S903 will bedescribed. After the TV-AF signal is retained in step S909, the cameracontrol unit 109 in step S910 acquires the latest TV-AF signal. Thecamera control unit 109 in step S911 compares the TV-AF signal retainedin step S909 with the new TV-AF signal acquired in step S910. When it isdetermined that the difference in the level of both signal is greaterthan or equal to a predetermined reference level, that is to say, whenthe camera control unit 109 determines that the fluctuation range of thesignal is greater than or equal to a reference range, the processproceeds to step S902, and minute driving is recommenced. Conversely,when it is determined that the difference in the level of the signals instep S911 is less than the predetermined reference level, the processproceeds to step S912. In step S912, the camera control unit 109 stopsthe focus lens 102 at that position, and then the processing returns tostep S910.

The minute driving executed in step S902 will be described next withreference to the flowchart in FIG. 9. Processing is commenced in stepS1001, and in step S1002, the TV-AF frame is set to thereby executeacquisition processing for the TV-AF signal. In the setting process forthe TV-AF frame, the detection frame is set based on the information forthe distance map to thereby include the area defined by the in-focusdistance within the depth of field (refer to FIG. 6). The camera controlunit 109 in step S1003 determines whether another object is present inaddition to the main object at the near-end depth based on the distancemap. FIG. 10A illustrates an example of a state in which an object isnot present at the near-end depth. When the depth of field is 1 to 2meters, the indicative range for the near-end depth is from 0.9 to 1.1meters, and 1.8 to 2.3 meters. In contrast, FIG. 10B illustrates anexample when an object is present in the near-end depth (refer to therectangular frame indicated by the sloping line). In the presentexample, it is determined that there is an object in a distance range of1.9 to 2.2 meters. When it is determined that the object is present atthe near-end depth, the process proceeds to step S1005. In this case,since it can be predicted that the presence of the object will cause aconspicuous change in the blurring resulting from driving of the focuslens 102, the lens driving amount per operation is changed, and asubtraction process is executed to reduce the driving amount incomparison to a predetermined amount. In this manner, the temporalvariation in a blurring amount overtime can be reduced, and it ispossible to improve variation in the blurring characteristics of theimage. Note that the predetermined amount is a lens driving amount whenanother object is not present in the near-end depth as determined in theresults of step S1003, and as illustrated in step S1004 describedhereafter, the predetermined amount corresponds to a lens driving amountwhen driving the focus lens 102 in normal driving control.

The camera control unit 109 in step S1004 sets a driving amount for thefocus lens 102 to the predetermined amount. The driving amount of thefocus lens 102 is normally determined using a ratio relative to thefocal depth, and is set to a value at which a change in focus is notevident on the screen in relation to an object which is originally infocus, even when the focus lens 102 is moved according to thepredetermined amount.

After steps S1004 and S1005, the process proceeds to step S1006, and thecamera control unit 109 compares the level of the TV-AF signal acquiredin step S1002 with the previous TV-AF signal. When the level of theTV-AF signal acquired in step S1002 is greater than the previous TV-AFsignal, the process proceeds to step S1007. When the level of thecurrent TV-AF signal is less than the previous TV-AF signal, the processproceeds to step S1008.

The camera control unit 109 in step S1008 determines whether or not toexecute minute driving so that all the in-focus distances in the depthselected by use of the distance map are included. In this manner, inaddition to merely adjusting the TV-AF signal, since all the in-focuspositions detected by the distance map can be searched, the cameracontrol unit 109 can search the real in-focus point without beingdeceived by a false peak related to the TV-AF signal. When all in-focuspositions have been searched, the process proceeds to step S1009, andwhen this is not the case, the process proceeds to step S1007.

The camera control unit 109 in step S1007 drives the focus lens by thepredetermined amount in the same direction as the previous lens drivingdirection (forward direction). On the other hand, the camera controlunit 109 in step S1009 drives the focus lens 102 by the predeterminedamount in a direction opposite to the previous lens driving direction.

After step S1007 or step S1009, the camera control unit 109 in stepS1010 determines whether the directions continuously determined as thein-focus direction over a predetermined number of times are allconfigured in the same direction. The predetermined number of timesindicates the reference value for direction discrimination, and is setin advance. When the determined direction is the same over thepredetermined number of times, the process proceeds to step S1014, andwhen the determined direction is not the same, the process proceeds tostep S1011. The camera control unit 109 in step S1011 determines whetheror not the focus lens 102 has repeated a reciprocating motion within apredetermined scope over a predetermined number of times. Thepredetermined number of times expresses a reference value fordetermination of the number of reciprocations, and is set in advance.The predetermined scope expresses the predetermined scope forcalculation of the number of times reciprocating motion of the focuslens 102 is executed. When it is determined that the focus lens 102 hasrepeated a reciprocating motion within a predetermined scope over thepredetermined number of times, the process proceeds to step S1013. Whenthis is not the case, the process proceeds to the return processing instep S1012. When the camera control unit 109 in step S1014 determinesthat the direction has been discriminated, the process proceeds to stepS1012. The determination result is used in step S904 in FIG. 8.Furthermore, when the camera control unit 109 in step S1013 determinesthat in-focus has been discriminated, the process proceeds to stepS1012. The determination result is used in step S9043 in FIG. 8.

The hill-climbing driving shown in step S905 in FIG. 8 will be describednext with reference to the flowchart in FIG. 11. The processing startsin step S1201, and the camera control unit 109 in step S1202 sets aTV-AF frame based on the distance map information to thereby acquire theTV-AF signal. The camera control unit 109 in step S1203 compares thelevel of the TV-AF signal acquired in step S1202 and the previous TV-AFsignal. When the level of the current TV-AF signal is greater than theprevious occasion, the process proceeds to step S1204. When the level ofthe current TV-AF signal is less than the previous occasion, the processproceeds to step S1205. The camera control unit 109 in the step S1204drives the focus lens 102 at a predetermined speed in the forwarddirection as the previous lens driving direction, and then proceeds tothe return processing in step S1208. On the other hand, the cameracontrol unit 109 in step S1205 determines whether or not the level ofthe TV-AF signal has been reduced from a value that exceeds its peakvalue. When the TV-AF signal level has exhibited a peak value and thenis subsequently reduced, the process proceeds to step S1207, and it isdetermined that the peak value was exceeded. The determination result isused in step S906 in FIG. 8. Conversely, when the TV-AF signal level instep S1205 exceeds the peak value and then is not reduced, the processproceeds to step S1206, and the camera control unit 109 drives the focuslens 102 at a predetermined speed in the direction that is opposite tothe previous lens driving direction. After step S1206 and step S1207,the process proceeds to the return processing in step S1208.

According to the first embodiment, improved automatic focus adjustmentperformance can also be obtained in an imaging system that has a shallowdepth of field by combining TV-AF control with focus adjustment controlbased on a distance map obtained using phase difference detection. Inother words, the focus lens is driven to enable high-speed recovery froma state associated with a large amount of blurring and to therebycorrectly focus to the real in-focusing point, and obtain an effect inwhich a conspicuous change in the amount of blurring in a backgroundimage can be suppressed.

Second Embodiment

Next, a second embodiment of the present invention will be described.The point of difference from the configuration of the first embodimentis that a signal is input to the TV-AF signal processing unit 504.Relevant components will be described with reference to FIG. 12. Thoseportions that are the same as the constituent portions of the firstembodiment illustrated in FIG. 4 are denoted using the same referencenumerals as those reference numerals already used above, and detaileddescription will not be repeated.

The signal after interpolation by the image interpolation processingunit 501 is sent through the AF gate switch 503 to the TV-AF signalprocessing unit 504. In other words, the signal input from the AF gateswitch 503 is a TV-AF signal that is free of the effect of defectivepixel portions corresponding to the position of the focus statedetection element. The TV-AF signal processing unit 504 obtains a valueexpressing the brightness of the image by processing of the TV-AF signaland outputs the information signal to the AF control unit 512. In thiscase, the role of the AF gate switch 503 is only to determine the AFarea based on the above distance map. The ON/OFF operation for the AFgate switch 503 is executed according to the control signal from the AFcontrol unit 512.

According to the second embodiment, information indicating thebrightness of the image is obtained from the signal after pixelinterpolation processing by the TV-AF control. Consequently, improvedautomatic focus adjustment performance is obtained also in relation toan image having a shallow depth of field by combination of a distancemap obtained by phase difference detection using an imaging element.

While the embodiments of the present invention have been described withreference to embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2010-108599 filed May 10, 2010 which is hereby incorporated by referenceherein in its entirety.

1. An imaging apparatus comprising: a focus state detection unitprovided in an imaging element and detecting a phase difference; asignal processing unit for generating a focus adjustment signal based onthe imaging signal outputted by the imaging element; and a control unitthat acquires an in-focus lens position in accordance with a focus lensbased on a focus deviation amount, the focus deviation amount calculatedfrom a detection result of the focus state detection unit, calculatesdistance information related to the in-focus distance on the imagescreen, and controls the driving of the focus lens based on the distanceinformation and the focus adjustment signal; wherein, when a differencebetween the in-focus lens position and the position of the focus lens atthe current time exceeds a threshold, the control unit drives the focuslens to the in-focus lens position, and when the difference between thein-focus lens position and the focus lens position at the current timeis less than or equal to the threshold, the control unit executes thein-focus control based on the focus adjustment signal.
 2. The imagingapparatus according to claim 1, wherein the control unit comprises: aphase-difference calculation processing unit for processing of adetection result from the focus state detection unit and calculates afocus deviation amount; a distance map generation processing unit thatcalculates the in-focus lens position based on the focus deviationamount, uses the in-focus lens position and the distance table togenerate map information expressing a distribution of the in-focusdistance in the imaging screen; and a focus adjustment control unit thatsets a detection frame for the focus state detection according to themap information, and executes drive control of the focus lens.
 3. Theimaging apparatus according to claim 2, wherein the focus adjustmentcontrol unit searches the proximity of the in-focus point according tothe map information, and shifts the focus lens to the in-focus pointbased on the focus adjustment signal.
 4. The imaging apparatus accordingto claim 3, wherein the focus adjustment control unit compares the casewhen it is determined that another object is present in addition to themain object in the near-end depth of the depth of field with the casewhen it is determined that another object is not present, and reducesthe drive amount of the focus lens in proximity to the in-focus point.5. The imaging apparatus according to claim 1, wherein the signalprocessing unit generates the focus adjustment signal using the imagingsignal for a pixel in a range that deletes horizontal lines that includethe focus state detection unit in the imaging element.
 6. The imagingapparatus according to claim 1, further comprising, a pixelinterpolation processing unit that calculates data corresponding to aposition of the focus state detection unit by interpolation using thedata for a pixel positioned in the periphery of the focus statedetection unit in the imaging element, wherein the signal processingunit generates the focus adjustment signal using the imaging signalobtained by interpolation of pixel by the pixel interpolation processingunit.
 7. A method for controlling an imaging apparatus, the imagingapparatus including a focus state detection unit provided in an imagingelement and detecting a phase difference, and a signal processing unitfor generating a focus adjustment signal based on the imaging signaloutputted by the imaging element, the method comprising the steps of:acquiring an in-focus lens position in accordance with a focus lensbased on a focus deviation amount calculated using a detection resultfrom the focus state detection unit to calculate distance informationrelated to the in-focus distance on the image screen; and driving thefocus lens to the in-focus lens position when a difference between thein-focus lens position and the position of the focus lens at the currenttime exceeds a threshold, and executing in-focus control based on thefocus adjustment signal when the difference between the in-focus lensposition and the focus lens position at the current time is less than orequal to the threshold.